In the production of high purity rare metal oxide powder such as zirconium oxide powder, zirconium present as the raw material Zircon sand is converted to soluble form after silica separation through the caustic fusion route. The said soluble form of zirconium is then dissolved in nitric acid and subjected to purification with respect to hafnium, titanium and other impurities using solvent extraction. This liquid-liquid extraction process is the heart of the plant and it comprises of three operations namely, selective extraction of zirconium from the feed solution, scrubbing or back extraction for removal of co-extracted hafnium and titanium from the solvent & finally stripping of zirconium from the loaded solvent using De-mineralized water (DMW) to generate pure zirconium nitrate solution.
Thus the said pure zirconium nitrate solution is further precipitated using ammonium hydroxide solution along with trace quantities of sulphuric acid. The resultant zirconium hydroxide is processed to provide an oxide product. In this process the nitrate present along with zirconium gets converted into ammonium nitrate and ammonium sulphate, which is required to be disposed as effluent as illustrated in FIG. 1.
Though the above mentioned solvent extraction process is capable of producing high purity zirconium nitrate solution, it has numerous drawbacks as discussed hereunder:
i) The process generates high amount of ammonium nitrate effluent in the order of 25000 liters for every MT of ZrO2 produced wherein regular disposal of this large quantity of effluent is mandatory and therefore problematic;
ii) The said effluent in being dilute containing only about 180 g/l of ammonium nitrate makes its disposal further commercially unattractive;
iii) Low stripping efficiency of De-mineralized water (DMW) requires the use of large amount of the stripping solution-DMW to avoid product losses through the solvent. Approximately about 1 g/l of zirconium remains unstripped in the stripped solvent using DMW as the stripping solution.
Thus as apparent and evident from the abovesaid that though the commonly known TBP (Tri-Butyl Phosphate)-nitrate solvent extraction process capable of producing high purity rare metal nitrate solution to provide for an active oxide product is highly prevalent, the said process is lined with a string of aforesaid disadvantages that need to be improved upon to necessitate the provision of a more convenient and efficient process that would lead to a substantial reduction in ammonium nitrate effluent volume to thereby increase its concentration to make its disposal commercially attractive, which said efficient process would also simultaneously induce low rare metal losses in the stripped solvent.